Method and Device for Forging Bevel Gear

ABSTRACT

A method and a device for forging a bevel gear. The device includes a punch, a work positioning and holding die positioning and holding a work placed on the placing surface of a lower die, and an outer burr removing die removing outer burrs produced on the outer peripheral surfaces of the teeth of the work. In the state of the work positioned and held at a prescribed position by the work positioning and holding die, the inner burrs and the outer burrs of the work are simultaneously removed by the integrated lowering operation of the punch and the outer burr removing die.

TECHNICAL FIELD

The present invention relates to a method and apparatus (device) forforging a bevel gear, for incorporation into the differential of anautomobile, for example.

BACKGROUND ART

Heretofore, there have been known methods of manufacturing bevel gearsfor use in automobile power transmitting connectors, e.g.,differentials, as well as dies for manufacturing such bevel gears (see,for example, Patent Document 1).

A bevel gear has conventionally been manufactured by the processdescribed below, as shown in FIGS. 12A through 12D.

A cylindrical stock 1 (see FIG. 12A) is forged in a single forging cycleor in a plurality of forging cycles so as to produce a preform 4 (seeFIG. 12B). The preform 4 has preliminary teeth 2, each of which includesa preliminary tooth tip surface 2 a that is progressively larger indiameter in one direction along its axis, and a preliminary tooth endsurface 2 b contiguous to the preliminary tooth tip surface 2 a. Thepreform 4 also has a preliminary main body 3, which includes apreliminary circumferential conical surface 3 a contiguous to thepreliminary tooth end surface 2 b, and which is progressively smaller indiameter in one direction along its axis.

Then, the preform 4 is pierced to produce an intermediate form 6 (seeFIG. 12C), having a through hole 5 defined therein along its centralaxis. Finally, the intermediate form 6 is sized into a bevel gear 7 (seeFIG. 12D,) wherein the teeth thereof are finished to acquire desireddimensions.

While the bevel gear is manufactured according to the above process, theteeth of the intermediate form 6 are sized so as to increase theiraccuracy, for thereby producing the bevel gear 7 having desired teeth.However, when the teeth are sized, due to the flowing material beingforged, outer burrs are formed along the tooth profile of the tooth endsurfaces.

According to Patent Document 1, since the outer burrs that occur alongthe tooth profile of the tooth end surface are inclined to the axis ofthe bevel gear, and are produced within regions where the tooth profileis of a complex shape including an involute curve, it is difficult toremove such outer burrs using a press, and hence the outer burrs must beremoved by a manual process (machining process) performed by the worker.According to Patent Document 1, the process of removing the outer burrsis time-consuming and lowers productivity.

Patent Document 2 discloses a forging press for forging a flange parthaving a shaft, and also discloses a technical concept in which bothouter burrs and inner burrs of a roughly formed part are simultaneouslycut off by a cutting blade and an upper punch of the forging press.

However, if such a technical concept, in which both outer burrs andinner burrs of a roughly formed part are simultaneously cut off asdisclosed by Patent Document 2, were to be applied to forging a bevelgear, then since the outer burrs that occur along the tooth profile ofthe tooth end surface are inclined with respect to the axis of the bevelgear, and further are produced within regions where the tooth profile isof a complex shape including an involute curve, it is necessary toremove the outer burrs along the tooth profile of the tooth end surfaceusing a deburring process, which is performed at the same time as thepiercing process, after the workpiece, as the intermediate form of thebevel gear, has been positioned in place.

In other words, when a bevel gear is forged, in order to remove outerburrs occurring along the tooth profile of the tooth end surface, it isnecessary to position and hold the workpiece in place, while removingthe outer burrs without causing damage to the tooth profile of theworkpiece that has been positioned and held. In contrast, the outerburrs disclosed in Patent Document 2 are of a simple ring shape that caneasily be removed.

Patent Document 1: Japanese Laid-Open Patent Publication No. 9-85385;and

Patent Document 2: Japanese Laid-Open Patent Publication No.2000-117628.

DISCLOSURE OF THE INVENTION

A general object of the present invention is to provide a method andapparatus for forging a bevel gear by means of a shortened manufacturingprocess, which increases productivity by simultaneously piercing anddeburring a workpiece while the workpiece is being appropriatelypositioned and held in place.

According to the present invention, a forging stock is forged in asingle forging cycle or in a plurality of forging cycles in order toproduce an intermediate form. The intermediate form is mounted as aworkpiece on a mount die of a lower die. The workpiece is positioned andheld in a predetermined position by a positioning and holding die, whichis fitted over a punch for displacement in unison with the punch.

While the intermediate form is positioned and held by the positioningand holding die, the intermediate form is pierced by the punch in orderto remove an inner burr thereof, and simultaneously, outer burrs of theintermediate form also are removed by an outer deburring die, which isfitted over the positioning and holding die for displacement in unisonwith the punch.

The intermediate form is positioned when engaging fingers provided on anend of the positioning and holding die engage within valleys locatedbetween the teeth of the intermediate form.

According to the present invention, when the punch, the workpiecepositioning and holding die, and the outer deburring die are displacedin unison with each other, the workpiece positioning and holding die,which projects a predetermined distance from the punch and the outerdeburring die toward the lower die, contacts the workpiece mounted onthe lower die, thereby holding the workpiece while it is positioned inthe predetermined position.

With the workpiece positioned and held by the workpiece positioning andholding die, the punch and the outer deburring die are displaced inunison with each other, so as to simultaneously remove both the innerburr and the outer burrs of the workpiece.

According to the present invention, furthermore, a forging stock isforged in a single forging cycle or in a plurality of forging cycles inorder to produce an intermediate form. The intermediate form is mountedas a workpiece on a mount die of a lower die. After circumferentialpositional errors of the workpiece have been corrected by a positioningand deburring die, which is fitted over a punch for displacement inunison with the punch, the workpiece is pressed against the lower die bya workpiece pressing die, which positions and holds the workpiece in apredetermined position.

While the intermediate form is positioned and held by the workpiecepressing die, the intermediate form is pierced by the punch in order toremove an inner burr thereof, and simultaneously, outer burrs of theintermediate form also are removed by the positioning and deburring die,which is fitted over the workpiece pressing die for displacement inunison with the punch.

The intermediate form is positioned when engaging protrusions on thepositioning and deburring die engage within valleys located between theteeth of the intermediate form.

According to the present invention, when the punch, the workpiecepressing die, and the positioning and deburring die are displaced inunison with each other, the positioning and deburring die, whichprojects a predetermined distance from the punch and the workpiecepressing die toward the lower die, contacts the workpiece mounted on thelower die, thereby holding the workpiece while it is positioned in thepredetermined position.

After the workpiece has been positioned and held by the positioning anddeburring die, and while the workpiece is positioned and held in thepredetermined position by the workpiece pressing die, the punch and theouter deburring die are displaced in unison with each other, so as tosimultaneously remove both the inner burr and the outer burrs of theworkpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1D are views showing a process of manufacturing a bevelgear according to an embodiment of the present invention;

FIG. 2 is a vertical cross-sectional view taken along the axialdirection of a forming apparatus according to the embodiment of thepresent invention;

FIG. 3 is a vertical cross-sectional view showing the manner in whichengaging fingers of a workpiece positioning and holding die of theforming apparatus shown in FIG. 2 are placed within valleys locatedbetween teeth of a workpiece;

FIG. 4 is a vertical cross-sectional view showing the manner in whichthe workpiece is positioned and held by the workpiece positioning andholding die of the forming apparatus shown in FIG. 2;

FIG. 5 is a vertical cross-sectional view showing the manner in whichinner burrs of the workpiece are removed by a punch of the formingapparatus shown in FIG. 2, and in which outer burrs of the workpiece areremoved by an outer burr cut-off die;

FIG. 6 is a bottom view of the workpiece positioning and holding die andthe outer burr cut-off die of the forming apparatus shown in FIG. 2;

FIG. 7 is a vertical cross-sectional view taken along an axial directionof a forming apparatus, according to another embodiment of the presentinvention;

FIG. 8 is a vertical cross-sectional view showing the manner in whichengaging fingers of a workpiece positioning and holding die of theforming apparatus shown in FIG. 7 are placed within valleys locatedbetween teeth of a workpiece;

FIG. 9 is a vertical cross-sectional view showing the manner in whichthe workpiece is positioned and held by the workpiece positioning andholding die of the forming apparatus shown in FIG. 7;

FIG. 10 is a vertical cross-sectional view showing the manner in whichinner burrs of the workpiece are removed by a punch of the formingapparatus shown in FIG. 7, and in which outer burrs of the workpiece areremoved by an outer burr cut-off die;

FIG. 11 is a bottom view of the workpiece positioning and holding dieand the outer burr cut-off die of the forming apparatus shown in FIG. 7;and

FIGS. 12A through 12D are views showing a conventional process formanufacturing a bevel gear.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIGS. 2 through 5, reference numeral 10 denotes a forming apparatusaccording to an embodiment of the present invention. The formingapparatus 10 is used in a forging process for forging a bevel gear 12(see FIG. 1D) as a result of forming a stock successively with aplurality of dies. The forming apparatus also is used to pierce (bore)and deburr the workpiece in a final process.

The forming apparatus 10 has a back plate (base) 16 fixedly mounted on abase plate, not shown, by a die holder 14, a hollow cylindrical lowerdie 18 disposed for displacement in a circumferential direction about anaxis of the back plate 16 and in vertical directions along the axis ofthe back plate 16, and a first helical spring (spring member) 20interposed between the back plate 16 and the lower die 18 for floatinglysupporting the lower die 18 with respect to the fixed back plate 16under spring forces.

The back plate 16 and the lower die 18 have a drop hole 24 definedvertically therethrough, which allows a cut-off inner burr 22 (see FIGS.1D and 5), to be described below, to drop therethrough. The back plate16 has an annular step 26 formed on an outer circumferential surfacethereof, which is engaged by an end of the first helical spring 20.

The lower die 18 has a mount surface 30 on its upper end for mounting aworkpiece 28 thereon. The mount surface 30 is complementary in shape tothe bottom surface of the workpiece 28. The lower die 18 also has, onits lower end, an annular flange 34 having an end face engaged by theother end of the first helical spring 20, wherein the annular flange 34is slidably displaceable vertically along an annular boss 32 of the backplate 16.

An annular surface 36 formed on an inner wall of the annular flange 34of the lower die 18 performs a stop function by abutting against anupper surface 37 of the annular boss 32 of the back plate 16, therebylimiting further downward displacement of the lower die 18 (see FIG. 5).

Since the mount surface 30 of the lower die 18 is complementary in shapeto the bottom surface of the bevel gear 12 to be manufactured, which isfree of a tooth profile surface, an intermediate form can easily bemounted on the mount surface 30.

The forming apparatus 10 also has a piercing punch 38 mounted on the ramof a press, not shown, and vertically movable for piercing a centralportion of the workpiece 28, a workpiece positioning and holding die 40fitted over the punch 38 and vertically displaceable along the punch 38,and an outer deburring die 42 fitted over the workpiece positioning andholding die 40. The punch 38 and the outer deburring die 42 areintegrally formed with each other and are fixed to the ram of thenon-illustrated press for displacement in unison with each other.

The outer deburring die 42 houses in a hollow space thereof a secondhelical spring 44, having stronger spring forces than the first helicalspring 20, and having a coil diameter that is greater than that of thefirst helical spring 20. The workpiece positioning and holding die 40 ispressed vertically downward by the second helical spring 44.

The workpiece positioning and holding die 40 has a larger-diameterportion 46 on an outer circumferential surface thereof. The workpiecepositioning and holding die 40 is prevented from being removed out ofthe outer deburring die 42 by the larger-diameter portion 46, when it isengaged by a tapered surface 48 that extends radially inwardly from aninner wall surface of the outer deburring die 42.

The workpiece positioning and holding die 40 is displaceableindependently of the punch 38 and the outer deburring die 42. Theworkpiece positioning and holding die 40 is lifted when it overcomes thespring forces of the second helical spring 44.

The workpiece positioning and holding die 40 has a smaller-diameterportion 50 on an inner wall surface thereof, providing a clearancebetween the workpiece positioning and holding die 40 and the outercircumferential surface of the punch 38 that extends centrally throughthe workpiece positioning and holding die 40.

The workpiece positioning and holding die 40 has a plurality of engagingfingers 52 formed on a lower end thereof, which project verticallydownward a predetermined distance from the lower end face of the outerdeburring die 42. Each of the engaging fingers 52 is of a substantiallytriangular cross-sectional shape having a slanted surface 54, whereinthe number of engaging fingers 52 corresponds to the number of valleys56 located between the teeth of the workpiece 28 (see FIG. 6). When theengaging fingers 52 enter along the valleys 56 located between the teethof the workpiece 28, and the slanted surfaces 54 of the engaging fingers52 come into contact with the valleys 56, the workpiece 28 is positionedin a predetermined position.

The workpiece positioning and holding die 40 has a pressing holder 58disposed on a lower end thereof near the engaging fingers 52, whereinthe pressing holder 58 comprises a hook-shaped step contiguous to theslanted surfaces 54. When the pressing holder 58 engages the uppersurface of the workpiece 28 and presses the workpiece 28 against thelower die 18, the workpiece 28 is held while being positioned in placein the predetermined position.

The outer deburring die 42 has, on a portion thereof near the engagingfingers 52, a plurality of cutting edges 62 for cutting off outer burrs60 produced between the teeth of the workpiece 28, wherein the cuttingedges 62 have substantially the same inside diameter as the outsidediameter A (see FIG. 2) of the workpiece 28 at a position between theteeth.

The forming apparatus 10 according to the embodiment of the presentinvention is basically constructed as described above. Operations andadvantages of the forming apparatus 10 shall be described below.

First, the cylindrical billet 64 shown in FIG. 1A is forged into apreform 68 having a bevel 66, as shown in FIG. 1B, using a first forgingdie, not shown. Then, using a second forging die, not shown, the preform68 is forged into an intermediate form 72 having teeth 70, as shown inFIG. 1C. The intermediate form 72 has thin outer burrs 60 that extendcontinuously along the outer circumference thereof between the teeth 70.

The forming apparatus 10 according to the present embodimentsimultaneously pierces the intermediate form 72 and removes the outerburrs from the intermediate form 72, which makes up the workpiece 28. Itshall be assumed that in an initial position, as shown in FIG. 2, thepunch 38, the workpiece positioning and holding die 40, and the outerdeburring die 42 are suspended in an upper position, which is spaced apredetermined distance from the lower die 18.

First, the intermediate form 72, which makes up the workpiece 28, isplaced on the mount surface 30 of the lower die 18 (see FIG. 2). At thistime, the bottom surface of the workpiece 28, which is free of anyteeth, may simply be placed on the mount surface 30 of the lower die 18,which is shaped complementarily to the shape of the bottom surface ofthe workpiece 28. The workpiece 28 does not need to be positionedexactly.

Then, the ram of the non-illustrated press is actuated in order to lowerthe punch 38. The workpiece positioning and holding die 40, and theouter deburring die 42 are lowered in unison from the initial positionuntil the engaging fingers 52 of the workpiece positioning and holdingdie 40, which project vertically downward by predetermined distancesfrom the punch 38 and the outer deburring die 42, are positioned withinthe respective valleys 56 located between the teeth.

The workpiece 28 is simply placed on the mount surface 30 of the lowerdie 18, and the lower die 18 is floatingly supported on the back plate16 under spring forces of the first helical spring 20. Therefore, thelower die 18 is angularly movable in the circumferential directionthereof.

Consequently, when the engaging fingers 52 of the workpiece positioningand holding die 40 enter into the valleys 56 and engage with the wallsurfaces of the valleys 56, any circumferential positional errors of theworkpiece 28 are corrected and the workpiece 28 is positioned in apredetermined position. Since the lower die 18 on which the workpiece 28is placed is angularly movable in the circumferential direction, theworkpiece 28 is easily positioned when the engaging fingers 52 simplyenter into the valleys 56.

Then, as shown in FIG. 4, upon further downward movement of the punch38, the workpiece positioning and holding die 40, and the outerdeburring die 42 in unison, the engaging fingers 52 of the workpiecepositioning and holding die 40 abut against the wall surfaces of thevalleys 56 of the workpiece 28, and the hook-shaped pressing holder 58abuts against the upper surface of the workpiece 28 and lowers theworkpiece 28 against the lower die 18. Thus, the workpiece 28 is heldwhile it is being positioned.

When the punch 38, the workpiece positioning and holding die 40, and theouter deburring die 42 are further lowered in unison, the lower die 18with the workpiece 28 positioned and held thereon is slightly displaceddownwardly in opposition to the spring forces of the first helicalspring 20. At this time, the annular surface 36 formed on the inner wallof the annular flange 34 of the lower die 18 performs a stop function byabutting against the upper surface 37 of the annular boss 32 of the backplate 16, thereby limiting downward displacement of the lower die 18. Asa result, the workpiece positioning and holding die 40, which pressesthe workpiece 28 against the lower die 18, is prevented from beinglowered, and the workpiece 28 is held as it is positioned in thepredetermined position.

Then, the punch 38 and the outer deburring die 42, except for theworkpiece positioning and holding die 40, are further lowered in unisonwith each other, in opposition to the spring forces of the secondhelical spring 44. As shown in FIG. 5, the inner burr 22 at the centerof the workpiece 28 is removed by the punch 38, while thin outer burrs60 that extend along the outer circumference of the workpiece 28 betweenthe teeth thereof are cut off by the cutting edges 62 of the outerdeburring die 42.

Stated otherwise, while the workpiece 28 is held, while being positionedin the predetermined position between the lower die 18 and the workpiecepositioning and holding die 40 under spring forces (pushing forces) ofthe second helical spring 44, only the punch 38 and the outer deburringdie 42 are lowered in unison with each other, thereby simultaneouslyremoving both the inner burr 22 and the outer burrs 60 from theworkpiece 28.

As a result, the bevel gear 12 shown in FIG. 1D is manufactured.

According to the present embodiment, while the workpiece 28 ispositioned and held against positional displacement by the workpiecepositioning and holding die 40 disposed radially between the punch 38and the outer deburring die 42, the inner burr 22 and the outer burrs 60are both simultaneously removed by the punch 38 and the outer deburringdie 42, respectively. Therefore, the process for manufacturing the bevelgear 12 is simplified, resulting in increased production efficiency andreduced production costs.

A forming apparatus 100 according to another embodiment of the presentinvention is shown in FIGS. 7 through 10. Parts of the forming apparatus100 that are identical to those of the forming apparatus 10 shown inFIG. 2 are denoted using identical reference characters, and shall notbe described in detail below.

The forming apparatus 100 according to the other embodiment has apiercing punch 38 mounted on the ram of a press, not shown, andvertically movable for piercing a central portion of a workpiece 28, aworkpiece pressing die 140 fitted over the punch 38 and verticallydisplaceable along the punch 38, and a positioning and deburring die 142fitted over the workpiece pressing die 140. The punch 38 and thepositioning and deburring die 142 are integrally formed with each otherand are fixed to the ram of the non-illustrated press for displacementin unison with each other.

The positioning and deburring die 142 houses within a hollow spacethereof a second helical spring 44 having stronger spring forces than afirst helical spring 20 that acts on a lower die 18, and which has acoil diameter greater than that of the first helical spring 20. Theworkpiece pressing die 140 is pressed vertically downward by the secondhelical spring 44.

The workpiece pressing die 140 is prevented from being removed out ofthe positioning and deburring die 142 by a larger-diameter portion 46 onthe outer circumferential surface of the workpiece pressing die 140,when it is engaged by a tapered surface 48 that extends radiallyinwardly from an inner wall surface of the positioning and deburring die142.

The workpiece pressing die 140 is displaceable independently of thepunch 38 and the positioning and deburring die 142. The workpiecepressing die 140 is lifted when it overcomes the spring forces of thesecond helical spring 44.

The workpiece pressing die 140 has a smaller-diameter portion 50 formedon the inner wall surface thereof, providing a clearance between theworkpiece pressing die 140 and the outer circumferential surface of thepunch 38 that extends centrally through the workpiece pressing die 140.

The workpiece pressing die 140 has a pressing holder 158 on a lower endthereof, which abuts against the upper surface of the workpiece 28. Thepressing holder 158 comprises a flat surface. When the pressing holder158 presses the workpiece 28 against the lower die 18, the workpiece 28is held while it is positioned in place in a predetermined position.

The positioning and deburring die 142 has a plurality of engagingprotrusions 152 formed on the lower end thereof, which projectvertically downward a predetermined distance from the lower end face(the pressing holder 158) of the workpiece pressing die 140. As shown inFIG. 11, each of the engaging protrusions 152 is of a substantiallytriangular cross-sectional shape having slanted surfaces 154. The numberof engaging protrusions 152 corresponds to the number of valleys 56 thatare formed between the teeth of the workpiece 28. When the engagingprotrusions 152 enter along the valleys 56 located between the teeth ofthe workpiece 28, and the slanted surfaces 154 of the engagingprotrusions 152 come into contact with the valleys 56, circumferentialpositional errors of the workpiece 28 are corrected, and the workpiece28 is positioned in a predetermined position.

The positioning and deburring die 142 includes, on a portion thereofnear to the engaging protrusions 152, a plurality of cutting edges 162for cutting off outer burrs 60 that are produced between the teeth ofthe workpiece 28, wherein the cutting edges 162 have substantially thesame inside diameter as the outside diameter A (see FIG. 11) of theworkpiece 28 at a position between the teeth.

The forming apparatus 100 according to the other embodiment of thepresent invention is basically constructed as described above.Operations and advantages of the forming apparatus 100 shall bedescribed below. It shall be assumed that in an initial position, asshown in FIG. 7, the punch 38, the workpiece pressing die 140, and thepositioning and deburring die 142 are suspended in an upper position,which is spaced a predetermined distance from the lower die 18.

First, the intermediate form 72, which makes up the workpiece 28, isplaced on the mount surface 30 of the lower die 18 (see FIG. 7). At thistime, the bottom surface of the workpiece 28, which is free of anyteeth, may simply be placed on the mount surface 30 of the lower die 18,which is shaped complementarily to the shape of the bottom surface ofthe workpiece 28. The workpiece 28 does not need to be positionedexactly.

Then, the ram of the non-illustrated press is actuated in order to lowerthe punch 38. The workpiece pressing die 140, and the positioning anddeburring die 142 are lowered in unison from the initial position untilthe engaging protrusions 152 of the positioning and deburring die 142,which project vertically downward by predetermined distances from thepunch 38 and the workpiece pressing die 140 and are disposed in anoutermost circumferential position, are positioned within the respectivevalleys 56 located between the teeth, as shown in FIG. 8.

The workpiece 28 is simply placed on the mount surface 30 of the lowerdie 18, and the lower die 18 is floatingly supported on the back plate16 under spring forces of the first helical spring 20. Therefore, thelower die 18 is angularly movable in the circumferential directionthereof.

Consequently, when the engaging protrusions 152 of the positioning anddeburring die 142 enter into the valleys 56 located between the teeth ofthe workpiece 28 and engage with the wall surfaces of the valleys 56,any circumferential positional errors of the workpiece 28 are correctedand the workpiece 28 is positioned in a predetermined position. Sincethe lower die 18 on which the workpiece 28 is placed is angularlymovable in the circumferential direction, the workpiece 28 is easilypositioned when the engaging protrusions 152 simply enter into thevalleys 56.

Then, as shown in FIG. 9, upon further downward movement of the punch38, the workpiece pressing die 140, and the positioning and deburringdie 142 in unison, the pressing holder 158 of the workpiece pressing die140 abuts against the upper surface of the workpiece 28 and presses theworkpiece 28 against the lower die 18, thereby holding the workpiece 28while it is being positioned.

When the punch 38, the workpiece pressing die 140, and the positioningand deburring die 142 are further lowered in unison, the lower die 18with the workpiece 28 positioned and held thereon is slightly displaceddownwardly in opposition to the spring forces of the first helicalspring 20. At this time, the annular surface 36 formed on the inner wallof the annular flange 34 of the lower die 18 performs a stop function byabutting against the upper surface 37 of the annular boss 32 of the backplate 16, thereby limiting downward displacement of the lower die 18. Asa result, the workpiece pressing die 140, which presses the workpiece 28against the lower die 18, is prevented from being lowered, and theworkpiece 28 is held as it is positioned in the predetermined position.

Then, the punch 38 and the positioning and deburring die 142, except forthe workpiece pressing die 140, are further lowered in unison with eachother, in opposition to the spring forces of the second helical spring44. As shown in FIG. 10, the inner burr 22 at the center of theworkpiece 28 is removed by the punch 38, while the thin outer burrs 60that extend along the outer circumference of the workpiece 28 betweenthe teeth thereof are cut off by the cutting edges 162 of thepositioning and deburring die 142.

Stated otherwise, while the workpiece 28 is held and positioned in thepredetermined position between the lower die 18 and the workpiecepressing die 140, under spring forces (pushing forces) produced by thesecond helical spring 44, only the punch 38 and the positioning anddeburring die 142 are lowered in unison with each other, for therebysimultaneously removing the inner burr 22 and the outer burrs 60 fromthe workpiece 28.

According to the other embodiment, after circumferential positionalerrors of the workpiece 28 have been corrected and the workpiece 28 ispositioned in a predetermined position, and further while the workpiece28 is positioned and held against positional displacement by theworkpiece pressing die 140 that is disposed radially between the punch38 and the positioning and deburring die 142, the inner burr 22 and theouter burrs 60 are simultaneously removed by the punch 38 and thepositioning and deburring die 142, respectively. Therefore, the processof manufacturing the bevel gear 12 is simplified for enabling increasedproduction efficiency, while also reducing production costs.

According to the other embodiment, furthermore, as a result of using thepositioning and deburring die 142, wherein slanted surfaces 154 of theengaging protrusions 152, which act to correct circumferentialpositional errors of the workpiece 28, and cutting edges 162 for cuttingoff the outer burrs 60 between the teeth are disposed contiguously, theworkpiece 28 is accurately positioned while the outer burrs 60 are cutoff from the workpiece continuously and smoothly.

1. An apparatus for forging a bevel gear, comprising: a lower die havinga mount surface for mounting a workpiece thereon, said lower die beingmounted on a base for rotation in a circumferential direction; a punchmounted for vertical movement with respect to said lower die, forpiercing a central portion of said workpiece in order to remove an innerburr thereof; a workpiece positioning and holding die fitted over saidpunch for displacement in unison with the punch, for pressing theworkpiece that is mounted on said mount surface of said lower dieagainst said lower die, for thereby positioning and holding theworkpiece; and an outer deburring die fitted over said workpiecepositioning and holding die and displaceable in unison with said punch,for removing outer burrs produced between teeth of said workpiece alongan outer circumference of said workpiece, wherein while said workpieceis positioned in a predetermined position and held in said position bysaid workpiece positioning and holding die, the inner burr and the outerburrs of said workpiece are simultaneously removed by movement of saidpunch and said outer deburring die in unison with each other.
 2. Theapparatus according to claim 1, further comprising a spring member bywhich said lower die is floatingly supported on said base.
 3. Theapparatus according to claim 1, wherein said workpiece positioning andholding die comprises engaging fingers for positioning said workpiece incircumferential directions thereof, by entering along and engagingwithin valleys located between the teeth of said workpiece, and apressing holder that abuts against an upper surface of said workpieceand presses said workpiece against the lower die to thereby hold saidworkpiece.
 4. The apparatus according to claim 1, wherein said lower dieincludes an annular flange having an end face that is engaged by an endof said spring member, and which is slidably displaceable verticallyalong an annular boss of said base.
 5. An apparatus for forging a bevelgear, comprising: a lower die having a mount surface for mounting aworkpiece thereon, said lower die being mounted on a base for rotationin a circumferential direction; a punch mounted for vertical movementwith respect to said lower die, for piercing a central portion of saidworkpiece in order to remove an inner burr thereof; a workpiece pressingdie fitted over said punch for displacement in unison with said punch,for pressing the workpiece that is mounted on said mount surface of saidlower die against said lower die, for thereby holding the workpiece; anda positioning and deburring die fitted over said workpiece pressing dieand displaceable in unison with said punch, for correctingcircumferential positional errors of said workpiece and positioning saidworkpiece, and for removing outer burrs produced between teeth of saidworkpiece along an outer circumference of said workpiece, wherein whilesaid workpiece positioned in a predetermined position is held in saidposition by said workpiece pressing die, the inner burr and the outerburrs of said workpiece are simultaneously removed by movement of saidpunch and said positioning and deburring die in unison with each other.6. The apparatus according to claim 5, further comprising a springmember by which said lower die is floatingly supported on said base. 7.The apparatus according to claim 5, wherein said positioning anddeburring die comprises engaging protrusions for positioning saidworkpiece in circumferential directions thereof by entering along andengaging within valleys located between the teeth of said workpiece, andcutting edges for removing the outer burrs produced between the teeth ofsaid workpiece along the outer circumference of said workpiece.
 8. Theapparatus according to claim 7, wherein said engaging protrusionsproject vertically downward a predetermined distance from a lower endface of said workpiece pressing die.
 9. A method of forging a bevelgear, comprising the steps of: forging a forging stock in a singleforging cycle or in a plurality of forging cycles, to thereby produce anintermediate form having teeth; placing said intermediate form on amount surface of a lower die, and positioning and holding saidintermediate form in a predetermining position with a positioning andholding die, which is fitted over a punch, for displacement in unisonwith said punch; and while said intermediate form is positioned and heldby said positioning and holding die, simultaneously piercing saidintermediate form in order to remove an inner burr thereof with saidpunch, and removing outer burrs of said intermediate form with an outerdeburring die, which is fitted over said positioning and holding die,for displacement in unison with said punch.
 10. The method according toclaim 9, wherein said intermediate form is positioned when engagingfingers disposed on an end of said positioning and holding die engagewithin valleys located between the teeth of said intermediate form. 11.A method of forging a bevel gear, comprising the steps of: forging aforging stock in a single forging cycle or in a plurality of forgingcycles, to thereby produce an intermediate form having teeth; placingsaid intermediate form on a mount surface of a lower die, correctingcircumferential positional errors of said intermediate form, andpositioning said intermediate form with a positioning and deburring die,which is fitted over a punch, for displacement in unison with the punch,and thereafter, positioning and holding said intermediate form in apredetermined position with a workpiece pressing die that is fitted insaid positioning and deburring die; and while said intermediate form ispositioned and held by said workpiece pressing die, simultaneouslypiercing said intermediate form in order to remove an inner burr thereofwith said punch, and removing outer burrs of said intermediate form withsaid positioning and deburring die, which is displaced in unison withthe punch.
 12. The method according to claim 11, wherein saidintermediate form is positioned when engaging protrusions disposed onsaid positioning and deburring die engage within valleys located betweenthe teeth of said intermediate form.